More information about PDC bit in drilling

Fishtail/drag bits were used in the early days of oil well drilling. Drag bits would not penetrate many of the formations which overlay deeper oil and gas reservoirs, and also were replaced by roller cone bits. This was realized in 1909. The cutting structure of the polycrystalline diamond compact (PDC) led to the drag bit competitive with the conventional roller cone and diamond bits.

PDC drill blanks

Drill blanks are included a layer of synthetic polycrystalline diamond bonded to a layer of cemented tungsten carbide using a high temperature, high-pressure bonding technique. Hardness and strength of the resulting blank can wear resistance of diamond and also the strength and impact resistance of tungsten carbide can complement it. Small self-sharpening and have no inherently weak cleavage planes, and also can result in massive fractures as in the large, single crystal diamonds in the diamond bits. For having optimal rate of penetration, the blanks are linked to tungsten carbide studs and the cutters are placed on the bit face. Then the bit body is used in the cones of tri-cone bits, and the face is then coated with a layer of tungsten carbide, to resist fluid erosion.  

Bit Design                                                 

For having to fish out of the hole, there are no bearings to wear out or broken cones. This is one of the advantages of PDC bits feature a steel or matrix head. Also bits extended gauge have inherent stabilization. Bits have several properties, including having a concave head. This head permitting several gauge and nose cutters to attack the rock simultaneously, increasing stabilization while decreasing the potential for deviation. There are three patterns of the cutters:

v Helical pattern on the face of the bit that known as an open face.

v A ribbed pattern, that has cutters on ribs less than one-inch above the bit face.

v A bladed patters, that has the cutters on blades, more than one-inch from the bit face.

PDC Bit Operating Parameters

PDC bits should use the bit’s hydraulics to flush the cuttings from under the bit to prevent balling. This will done for minimizing erosion of the body near the nozzle area and maximize cleaning. The range of the Optimum hydraulic is between 2.0 to 4.0 hydraulic horsepower per square inch. And the standard sizes of the interchangeable jet nozzles are from 8/32’s to 14/32’s. The cutting structure can control the Bit life. To medium formations such as shale, chalks, limestone, clays, salts and anhydrite, this combination is very important. The chances of deviation will reduce because the High rotary speeds provide better drill rates. The increasing of the string life and lower stress on the drill string are because of the Lighter weight-on-bit. Because of fewer drill collars are required in directional holes, they have less drag.  You have to be careful when choosing bits. If you use the bits correctly, it will eventually be usable in more than one well.

PDC Bit Drilling Parameters

To use drilling PDC bits correctly, you should pay attention to the following points:

1- Examine the damage caused by the previous bit. For example, check the hole of the previous bit and if it has junk, empty it.

2- When replacing a bit, do not roll it on the rig floor as doing so will shorten the life of the bit.

3- Bits do not have flexibility and can be damaged by impact on surfaces.

4- Before entering the hole, first apply the ream. Move forward at a rotational speed of 60 degrees.

5- To avoid plugging the bit with any fill, the last joint should be washed down slowly at full flow and 40-50 rpm.

6- For starting the drilling, you have to have speed up to 60 and approach bottom. You have to use Light weight to cut a new hole pattern.

7- There is no limit to the speed of rotation, as long as it does not damage the rest of the drill.

8- In the absence of mass accumulation, the formation may not be suitable for PDC bits.

9- Wash back down the bit after making a connection.

10- Rate of penetration suddenly decreases, a change in speed and a change in bit weight will be helpful.

11- The location of the wear is important. If it is on the outside, the penetration rate and torque will decrease and the standpipe pressure will increase. If it is on the gauge portion, the penetration rate will decrease.  

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